A head for spraying apparatus which discharges a high velocity stream of atomized electrostatically charged liquid droplets.
Apparatus to atomize, electrostatically charge, and discharge a high velocity stream of air and charged liquid droplets (a xe2x80x9cfluidxe2x80x9d stream) in an orderly pattern is known. Among the advantages of such apparatus in agricultural applications is the property of the charged droplets to deposit on all surfaces, top and bottom of leaves for example. This gives maximum coverage and protection for the plant or crop which is sprayed. An example of one known apparatus for this purpose is shown in Inculet et al U.S. Pat. No. 4,673,132. Spraying apparatus according to this instant invention offers advantages not provided by the Inculet sprayer.
The conditions of use of crop spraying equipment are often quite severe. Generally the spray heads are heavy and are supported on booms or arms. In use they can and do hit on hard surfaces, which tend to damage the head structure. Ordinarily dents and penetration of agriculture equipment surfaces are not objectionable. However, electrostatic sprayers involve situations which are not ordinary. They operate at high voltage such as 12,000 volts, and the operator must be protected from them. Also, correct distribution of the droplets is essential in order that all plant surfaces in range are properly and uniformly covered. For this, precise conduit and nozzle dimensions are essential. A dent, deformation, or perforation can result in a substantial loss of efficiency wherein portions of the flow might not be suitably supplied with an additive such as an insecticide, or the spray pattern may not be correctly formed, or if it is, the electrostatic charge may not be optimally consistent.
Spray heads of this type are frequently made of fiberglass. This material is useful because it has insulating properties. However, it does have the tendency to pick up moisture, and is readily deformable. This can result in undesirable degradation of the quality of discharge as well as the pattern of the discharged stream.
In addition there is a rather unexpected consequence of the use of fiberglass. These spray heads are generally used near combustion engines and some of their exhaust gases, in which substantial amounts of carbon are contained, reach the intake of the spray apparatus. Over a period of time which really is not very long, layer of carbon soot becomes lodged on the fiberglass surface which is practically impossible to remove. Ultimately it results in shorting out of the circuitry, or at least in degradation of performance. Even more the plexiglass tends to be porous, permeable and have a rough surface. The roughness of surface can have an undesirable affect on what should be a smooth flow. The permeability can result in carry-over of traces on previous usage to the next.
In contrast, the smooth, hard surfaces of this invention are interrupted only by readily cleaned electrode surfaces. They do not harbor carbon deposits in small craters because there are none. They are non-porous and not readily damaged or deformed.
As a further advantage, the discharge configuration and the electrode configuration can be changed by the simple replacement of one small part of the structure (the panel), and it can be adjustable if desired. When a fiberglass nozzle is used, it is necessary to change the entire structure.
It is an object of this invention to provide a spray head for an electrostatic sprayer which is structurally resistant to deformation and penetration, which is readily cleaned, and which can readily be manufactured accurately and economically.
Another object of this invention is to provide a panel bearing the electrodes for charging the droplets, which can readily be manufactured in an assortment of channel shapes, sizes, and electrode patterns, which can economically be manufactured, replaced if damaged, and adjusted or replaced with another shape to provide different spray patterns.
A spray head for spraying apparatus according to this invention comprises a body formed as a conduit leading from an inlet end to a discharge end at which it forms a discharge pattern. A high velocity stream of air is injected into the head at its inlet end and flows through the conduit to its discharge end. Adjacent to the discharge end, a rank of injection nozzles injects liquid into the air stream, and adjacent to the nozzles, a rank of electrodes is formed in the wall of the conduit.
The body is a rigid metal structure, adapted to be attached to a supporting mechanism such as a boom for manipulation. Its internal surfaces are disposed and arranged to direct a rapidly-moving air stream toward the discharge end. A plurality of injector nozzles is mounted to the body adjacent to the discharge end. These nozzles inject liquid into the conduit, there to be sheared by the air stream and form a myriad of small droplets to be distributed throughout the air stream. The air stream also flows past electrodes to become electrostatically charged.
A feature of this invention is to provide a separable panel adjacent to the discharge end. It forms part of the wall of the conduit at the discharge end. It exposes on its inside surface a plurality of electrodes. This panel is comprised of an electrically conductive hard metal, for example 316 stainless steel, with an adherent and tough cover of insulation. This panel is highly resistant to deformation, and the cover is highly resistant to penetration.
The panel is fitted to and attached to the body. It is externally insulated, so the body need not itself be coated with insulation. As structure, the panel is initially completely covered by the tough layer of insulating material. The panel includes a plurality of electrodes formed as ports, comprising the metal structure exposed through openings formed in the insulating layer. The metal structure is connected to a source of voltage. These electrodes are patch-like, and are exposed to the air stream.
According to a feature of the invention, the ports are formed by milling away the insulating layer to expose correctly-shaped and correctly-located electrodes. Thus panel blanks can be made to provide different numbers, shapes, and arrangements of electrodes merely by milling away some of the insulating material at the appropriate locations and then using the correct panel.
According to a preferred but optional feature of the invention, the panel is trough-like with a pair of side walls for adjustable attachment to the body.
The above and other features of this invention will be fully understood from the following detailed description and the accompanying drawings, in which: